CVE-2025-13086Network attack vector

Denial of service via inverted HMAC comparison

Published Dec 3, 2025 · Updated Dec 12, 2025

Improper source-address validation in OpenVPN 2.6.0 through 2.6.15 and 2.7_alpha1 through 2.7_rc1 allows remote attackers to interrupt service. The three-way handshake's HMAC-cookie verification interprets the memcmp result backwards, accepting every cookie instead of rejecting mismatches. Spoofed TLS handshake packets can consume server state until new VPN connections are refused, without exposing or altering tunnel data.

CVSS severity7.5
High
EPSS probability0.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper source-address validation in OpenVPN 2.6.0 through 2.6.15 and 2.7_alpha1 through 2.7_rc1 allows remote attackers to interrupt service. The three-way handshake's HMAC-cookie verification interprets the memcmp result backwards, accepting every cookie instead of rejecting mismatches. Spoofed TLS handshake packets can consume server state until new VPN connections are refused, without exposing or altering tunnel data.

The record

CVE
CVE-2025-13086
Published
Dec 3, 2025
Updated
Dec 12, 2025
Vendor
OpenVPN Inc.
Product
OpenVPN
Classifications
CWE-940, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 3, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 12, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.6.0 <=2.6.15
  2. Affected versionversion=2.7_alpha1 <=2.7_rc1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenVPN Inc. · OpenVPNversion=2.6.0 <=2.6.15; version=2.7_alpha1 <=2.7_rc1

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.6OpenVPN CNACVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-940Improper Verification of Source of a Communication Channel
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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